diff --git a/src/app/(dashboard)/[portSlug]/admin/branding/page.tsx b/src/app/(dashboard)/[portSlug]/admin/branding/page.tsx
index 2aedd4cb..3af67355 100644
--- a/src/app/(dashboard)/[portSlug]/admin/branding/page.tsx
+++ b/src/app/(dashboard)/[portSlug]/admin/branding/page.tsx
@@ -52,6 +52,10 @@ const FIELDS: SettingFieldDef[] = [
     description:
       'Blurred photo shown behind the white email card and the auth-shell (login / reset password) pages. Leave blank to render a plain off-white backdrop. Recommended: 1920x1080 JPG, pre-blurred to ~20px gaussian so it reads as a soft background even on small clients.',
     type: 'image-upload',
+    // 16:9 — landscape. Without an explicit aspect, the cropper falls
+    // back to 1:1 and renders a circular mask (intended for avatars),
+    // which is the wrong UX for a viewport-cover background.
+    imageAspect: 16 / 9,
     defaultValue: '',
   },
   {
diff --git a/src/app/api/v1/admin/branding/logo/route.ts b/src/app/api/v1/admin/branding/logo/route.ts
index 320fd4f1..5a56d0f6 100644
--- a/src/app/api/v1/admin/branding/logo/route.ts
+++ b/src/app/api/v1/admin/branding/logo/route.ts
@@ -51,10 +51,13 @@ export const GET = withAuth(
         return NextResponse.json({ data: null });
       }
       const baseUrl = env.APP_URL.replace(/\/+$/, '');
+      // Stream from the public-by-id surface (gated on `category='branding'`)
+      // so the URL works as a direct `<img src>` — the authenticated
+      // `/api/v1/files/<id>/preview` returns JSON, not image bytes.
       return NextResponse.json({
         data: {
           fileId: file.id,
-          previewUrl: `${baseUrl}/api/v1/files/${file.id}/preview`,
+          previewUrl: `${baseUrl}/api/public/files/${file.id}`,
           sizeBytes: file.sizeBytes,
           mimeType: file.mimeType,
         },
@@ -96,7 +99,7 @@ export const POST = withAuth(
       return NextResponse.json({
         data: {
           fileId: result.fileId,
-          previewUrl: `${baseUrl}/api/v1/files/${result.fileId}/preview`,
+          previewUrl: `${baseUrl}/api/public/files/${result.fileId}`,
           warnings: result.warnings,
           finalDimensions: processed.finalDimensions,
           finalBytes: processed.finalBytes,
diff --git a/src/app/api/v1/admin/settings/image/route.ts b/src/app/api/v1/admin/settings/image/route.ts
index 55fafe65..283dc94d 100644
--- a/src/app/api/v1/admin/settings/image/route.ts
+++ b/src/app/api/v1/admin/settings/image/route.ts
@@ -40,17 +40,31 @@ export const POST = withAuth(
       if (!port) throw new ValidationError('No active port');
 
       const buffer = Buffer.from(await fileEntry.arrayBuffer());
+      // Pick the storage filename's extension from the upload's MIME so
+      // PNG uploads aren't silently relabelled `.jpg` (the previous
+      // hardcoded extension flattened alpha-transparent logos).
+      const mimeType = fileEntry.type || 'image/jpeg';
+      const ext =
+        mimeType === 'image/png'
+          ? 'png'
+          : mimeType === 'image/webp'
+            ? 'webp'
+            : mimeType === 'image/gif'
+              ? 'gif'
+              : mimeType === 'image/avif'
+                ? 'avif'
+                : 'jpg';
       const record = await uploadFile(
         port.id,
         port.slug,
         {
           buffer,
-          originalName: fileEntry.name || 'branding.jpg',
-          mimeType: fileEntry.type || 'image/jpeg',
+          originalName: fileEntry.name || `branding.${ext}`,
+          mimeType,
           size: fileEntry.size,
         },
         {
-          filename: `branding-${Date.now()}.jpg`,
+          filename: `branding-${Date.now()}.${ext}`,
           category: 'branding',
           entityType: 'port',
           entityId: port.id,
diff --git a/src/app/api/v1/me/avatar/route.ts b/src/app/api/v1/me/avatar/route.ts
index 7fa8a513..a323e7a4 100644
--- a/src/app/api/v1/me/avatar/route.ts
+++ b/src/app/api/v1/me/avatar/route.ts
@@ -45,17 +45,31 @@ export const POST = withAuth(async (req, ctx) => {
     if (!portId) throw new ValidationError('No active port');
 
     const buffer = Buffer.from(await fileEntry.arrayBuffer());
+    // Pick the storage filename's extension from the upload's MIME so
+    // PNG uploads aren't silently relabelled `.jpg` (which would strip
+    // the alpha-channel signal from the storage layer).
+    const mimeType = fileEntry.type || 'image/jpeg';
+    const ext =
+      mimeType === 'image/png'
+        ? 'png'
+        : mimeType === 'image/webp'
+          ? 'webp'
+          : mimeType === 'image/gif'
+            ? 'gif'
+            : mimeType === 'image/avif'
+              ? 'avif'
+              : 'jpg';
     const record = await uploadFile(
       portId,
       portSlug,
       {
         buffer,
-        originalName: fileEntry.name || 'avatar.jpg',
-        mimeType: fileEntry.type || 'image/jpeg',
+        originalName: fileEntry.name || `avatar.${ext}`,
+        mimeType,
         size: fileEntry.size,
       },
       {
-        filename: `avatar-${ctx.userId}.jpg`,
+        filename: `avatar-${ctx.userId}.${ext}`,
         category: 'avatar',
         entityType: 'user',
         entityId: ctx.userId,
diff --git a/src/components/admin/branding/pdf-logo-uploader.tsx b/src/components/admin/branding/pdf-logo-uploader.tsx
index 99b4f7b3..57db78c4 100644
--- a/src/components/admin/branding/pdf-logo-uploader.tsx
+++ b/src/components/admin/branding/pdf-logo-uploader.tsx
@@ -10,6 +10,7 @@ import { Button } from '@/components/ui/button';
 import { Card, CardContent, CardDescription, CardHeader, CardTitle } from '@/components/ui/card';
 import { Label } from '@/components/ui/label';
 import { toastError } from '@/lib/api/toast-error';
+import { resolvePortIdFromSlug } from '@/lib/api/client';
 import { toast } from 'sonner';
 import { useConfirmation } from '@/hooks/use-confirmation';
 
@@ -40,6 +41,26 @@ interface UploadResult {
   originalFormat: string;
 }
 
+/**
+ * Raw `fetch()` doesn't carry the `X-Port-Id` header that
+ * `apiFetch` injects, so the branding endpoints (which require port
+ * context) 400 with "No active port". We can't swap to `apiFetch`
+ * here because the upload payload is `FormData`, not JSON. So resolve
+ * the active port from the URL the same way `apiFetch` does and
+ * attach the header manually.
+ */
+async function brandingHeaders(): Promise<Headers> {
+  const headers = new Headers();
+  if (typeof window === 'undefined') return headers;
+  const slug = window.location.pathname.split('/').filter(Boolean)[0];
+  if (!slug || slug === 'login' || slug === 'portal' || slug === 'api' || slug === 'dashboard') {
+    return headers;
+  }
+  const portId = await resolvePortIdFromSlug(slug);
+  if (portId) headers.set('X-Port-Id', portId);
+  return headers;
+}
+
 const WARNING_LABELS: Record<string, string> = {
   trimmed: 'Auto-trimmed whitespace borders',
   resized: 'Downscaled for size',
@@ -82,7 +103,8 @@ export function PdfLogoUploader() {
   async function refresh() {
     setLoading(true);
     try {
-      const res = await fetch('/api/v1/admin/branding/logo');
+      const headers = await brandingHeaders();
+      const res = await fetch('/api/v1/admin/branding/logo', { headers });
       if (!res.ok) throw new Error(`GET ${res.status}`);
       const body = (await res.json()) as { data: CurrentLogo | null };
       setCurrent(body.data ?? null);
@@ -139,7 +161,12 @@ export function PdfLogoUploader() {
           }),
         );
       }
-      const res = await fetch('/api/v1/admin/branding/logo', { method: 'POST', body: fd });
+      const headers = await brandingHeaders();
+      const res = await fetch('/api/v1/admin/branding/logo', {
+        method: 'POST',
+        headers,
+        body: fd,
+      });
       const body = (await res.json()) as { data: UploadResult } | { error?: { message?: string } };
       if (!res.ok) {
         const message = ('error' in body && body.error?.message) || `Upload failed (${res.status})`;
@@ -170,7 +197,8 @@ export function PdfLogoUploader() {
     if (!ok) return;
     setWorking(true);
     try {
-      const res = await fetch('/api/v1/admin/branding/logo', { method: 'DELETE' });
+      const headers = await brandingHeaders();
+      const res = await fetch('/api/v1/admin/branding/logo', { method: 'DELETE', headers });
       if (!res.ok && res.status !== 204) throw new Error(`DELETE ${res.status}`);
       toast.success('Logo removed');
       setCurrent(null);
diff --git a/src/components/admin/shared/settings-form-card.tsx b/src/components/admin/shared/settings-form-card.tsx
index 14d5ca4a..b00fcb5c 100644
--- a/src/components/admin/shared/settings-form-card.tsx
+++ b/src/components/admin/shared/settings-form-card.tsx
@@ -19,7 +19,7 @@ import {
   SelectTrigger,
   SelectValue,
 } from '@/components/ui/select';
-import { apiFetch } from '@/lib/api/client';
+import { apiFetch, resolvePortIdFromSlug } from '@/lib/api/client';
 import { toastError } from '@/lib/api/toast-error';
 
 export type SettingFieldType =
@@ -49,6 +49,11 @@ export interface SettingFieldDef {
   defaultTemplate?: string;
   /** For 'image-upload' fields: cropper aspect ratio. */
   imageAspect?: number;
+  /** For 'image-upload' fields: output format. Default 'jpeg' (smaller
+   *  files, good for photos / backgrounds). Use 'png' for logos with
+   *  transparency — JPEG has no alpha channel, so transparent pixels
+   *  composite against black on export. */
+  imageFormat?: 'jpeg' | 'png';
 }
 
 interface SettingsRowResponse {
@@ -399,8 +404,27 @@ function ImageUploadField({
 
   async function uploadCropped(blob: Blob) {
     const fd = new FormData();
-    fd.append('file', new File([blob], 'image.jpg', { type: 'image/jpeg' }));
-    const res = await fetch('/api/v1/admin/settings/image', { method: 'POST', body: fd });
+    // Trust the blob's own MIME — the cropper auto-picks PNG when the
+    // source had alpha, JPEG otherwise. Hardcoding to JPEG here threw
+    // away the alpha channel on transparent logos.
+    const mime = blob.type || 'image/jpeg';
+    const ext = mime === 'image/png' ? 'png' : 'jpg';
+    fd.append('file', new File([blob], `image.${ext}`, { type: mime }));
+    // Raw fetch (not apiFetch — FormData body) → manually attach the
+    // X-Port-Id header that the admin settings route requires.
+    const headers = new Headers();
+    if (typeof window !== 'undefined') {
+      const slug = window.location.pathname.split('/').filter(Boolean)[0];
+      if (slug && slug !== 'login' && slug !== 'portal' && slug !== 'api' && slug !== 'dashboard') {
+        const portId = await resolvePortIdFromSlug(slug);
+        if (portId) headers.set('X-Port-Id', portId);
+      }
+    }
+    const res = await fetch('/api/v1/admin/settings/image', {
+      method: 'POST',
+      headers,
+      body: fd,
+    });
     if (!res.ok) {
       const err = (await res.json().catch(() => ({}))) as { error?: { message?: string } };
       throw new Error(err.error?.message ?? 'Image upload failed');
@@ -470,6 +494,7 @@ function ImageUploadField({
         file={pendingFile}
         aspect={field.imageAspect ?? 1}
         outputWidth={field.imageAspect && field.imageAspect > 1 ? 1024 : 512}
+        outputFormat={field.imageFormat ?? 'auto'}
         title={`Crop ${field.label.toLowerCase()}`}
         onUpload={uploadCropped}
       />
diff --git a/src/components/settings/user-settings.tsx b/src/components/settings/user-settings.tsx
index b64d6496..8514be26 100644
--- a/src/components/settings/user-settings.tsx
+++ b/src/components/settings/user-settings.tsx
@@ -118,7 +118,11 @@ export function UserSettings() {
 
   async function uploadAvatar(blob: Blob) {
     const fd = new FormData();
-    fd.append('file', new File([blob], 'avatar.jpg', { type: 'image/jpeg' }));
+    // Preserve the cropper's chosen format — a transparent PNG uploaded
+    // as JPEG composites the alpha against black on export.
+    const mime = blob.type || 'image/jpeg';
+    const ext = mime === 'image/png' ? 'png' : 'jpg';
+    fd.append('file', new File([blob], `avatar.${ext}`, { type: mime }));
     const res = await fetch('/api/v1/me/avatar', { method: 'POST', body: fd });
     if (!res.ok) throw new Error('Avatar upload failed');
     const json = (await res.json()) as { data: { avatarFileId: string } };
diff --git a/src/components/shared/image-cropper-dialog.tsx b/src/components/shared/image-cropper-dialog.tsx
index 78eb9797..8d7fa10d 100644
--- a/src/components/shared/image-cropper-dialog.tsx
+++ b/src/components/shared/image-cropper-dialog.tsx
@@ -23,10 +23,14 @@ export interface ImageCropperDialogProps {
   /** Aspect ratio for the crop frame. 1 = square (avatars), 4 = wide
    *  banners. Defaults to 1. */
   aspect?: number;
-  /** Output JPEG quality 0-1. Default 0.85. */
+  /** Output JPEG quality 0-1. Default 0.85. Ignored for PNG. */
   outputQuality?: number;
   /** Output width in pixels (height derived from aspect). Default 512. */
   outputWidth?: number;
+  /** Output format. 'auto' (default) preserves alpha: PNG output when
+   *  the source is PNG/GIF/WebP/AVIF, JPEG otherwise. Override to force
+   *  a specific format. */
+  outputFormat?: 'auto' | 'jpeg' | 'png';
   /** Async upload handler — receives the cropped Blob. Cropper closes on
    *  success; toasts on error. */
   onUpload: (blob: Blob) => Promise<void>;
@@ -34,6 +38,14 @@ export interface ImageCropperDialogProps {
   title?: string;
 }
 
+/**
+ * MIME types that carry an alpha channel. A PNG source dropped through a
+ * JPEG-output canvas composites transparent pixels against black on
+ * export — destroying the design intent of any logo with transparency.
+ * Default to PNG output whenever the source could have had alpha.
+ */
+const ALPHA_CAPABLE_MIME = new Set(['image/png', 'image/gif', 'image/webp', 'image/avif']);
+
 /**
  * Reusable crop-then-upload modal. Renders a draggable/zoomable crop
  * frame over the picked file, then writes the cropped pixels to a
@@ -49,6 +61,7 @@ export function ImageCropperDialog({
   aspect = 1,
   outputQuality = 0.85,
   outputWidth = 512,
+  outputFormat = 'auto',
   onUpload,
   title = 'Crop image',
 }: ImageCropperDialogProps) {
@@ -64,10 +77,23 @@ export function ImageCropperDialog({
   }, []);
 
   async function handleUpload() {
-    if (!objectUrl || !pixels) return;
+    if (!objectUrl || !pixels || !file) return;
     setUploading(true);
     try {
-      const blob = await renderCrop(objectUrl, pixels, aspect, outputWidth, outputQuality);
+      const resolvedFormat: 'jpeg' | 'png' =
+        outputFormat === 'auto'
+          ? ALPHA_CAPABLE_MIME.has(file.type)
+            ? 'png'
+            : 'jpeg'
+          : outputFormat;
+      const blob = await renderCrop(
+        objectUrl,
+        pixels,
+        aspect,
+        outputWidth,
+        outputQuality,
+        resolvedFormat,
+      );
       await onUpload(blob);
       onOpenChange(false);
     } catch (err) {
@@ -146,8 +172,9 @@ export function ImageCropperDialog({
 
 /**
  * Crop the source image at `pixels`, resize to `outputWidth`×
- * (outputWidth/aspect), and return as a JPEG Blob. Async because
- * <img> needs an onload event before we can drawImage.
+ * (outputWidth/aspect), and return as a JPEG or PNG Blob. Async because
+ * <img> needs an onload event before we can drawImage. PNG preserves
+ * alpha for logos; JPEG is smaller for photos / backgrounds.
  */
 async function renderCrop(
   src: string,
@@ -155,6 +182,7 @@ async function renderCrop(
   aspect: number,
   outputWidth: number,
   quality: number,
+  format: 'jpeg' | 'png',
 ): Promise<Blob> {
   const image = await loadImage(src);
   const canvas = document.createElement('canvas');
@@ -174,11 +202,13 @@ async function renderCrop(
     outputWidth,
     outputHeight,
   );
+  const mime = format === 'png' ? 'image/png' : 'image/jpeg';
   return await new Promise<Blob>((resolve, reject) => {
     canvas.toBlob(
       (b) => (b ? resolve(b) : reject(new Error('Canvas toBlob returned null'))),
-      'image/jpeg',
-      quality,
+      mime,
+      // toBlob's quality param applies to JPEG/WebP only; PNG ignores it.
+      format === 'jpeg' ? quality : undefined,
     );
   });
 }
diff --git a/src/lib/api/client.ts b/src/lib/api/client.ts
index b67b8ae6..55894b9b 100644
--- a/src/lib/api/client.ts
+++ b/src/lib/api/client.ts
@@ -15,7 +15,7 @@ const slugToIdCache = new Map<string, string>();
  *  trip instead of N. */
 let inFlightPortsLookup: Promise<Array<{ id: string; slug: string }> | null> | null = null;
 
-async function resolvePortIdFromSlug(slug: string): Promise<string | null> {
+export async function resolvePortIdFromSlug(slug: string): Promise<string | null> {
   const cached = slugToIdCache.get(slug);
   if (cached) return cached;
   if (!inFlightPortsLookup) {